1. Field of the Invention
This invention relates an electrochemical storage cell or battery with at least one anode chamber for alkali metal as the anolyte and at least one cathode chamber for the sulfur-containing catholyte substance with the anolyte and catholyte separated from each other by an alkali-ion conducting solid electrolyte and bounded by a cellwall of a light metal which also functions as a current collector.
2. Description of the Prior Art
Storage cells of the above mentioned design present a considerable simplification as to their construction by using the cell wall as current collector. A further advantage results also from the use of light metals or the alloys of light metals for the cellwalls, which leads to high power-density of the storage cells or batteries.
However, a considerable disadvantage of such storage cells is due to the corrosion of the cellwall material by the catholyte substance, particularly by the sulfur or sodium polysulfide melt.
It was noted that light metal alloys corrode much faster in an electric field, particularly in the form of dangerous localized pitting corrosion. To overcome this problem, the suggestion was made (German Published Non-Prosecuted Application 2,457,418) to dispose a screening electrode made of a more corrosion resisting material, particularly graphite, in front of the cellwall.
Attempts were made to protect the light metal cellwalls of such storage cells from corrosion by means of a cover layer of MoS.sub.2, U.S. Pat. No. 3,749,603 and also to put layers of cobalt-or chromium sulfides onto the light-metal cellwalls.
The above mentioned procedures improved the behaviour with respect to corrosion for short periods, however, after longer time spans new disadvantages turned up. In this connection the rising of the interior resistance of the cell must be mentioned particularly. Also other negative symptoms appeared because of a lack of knowledge of the required material parameters necessary for the complex situation of this application.